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boric oxide combines with a few strongly acidic oxides (8. par. 455). Several salts of yttrium, scandium, lanthanum, and ytterbium have been prepared ; few basic salts are known. The sulphates seem all to combine with sulphate of potassium to form double salts; these are not alums; they generally have the composition M (SO),.3K SO,

So far as the odd-series elements of Group ÍII.' have been ex- 459 amined, it appears that the four elements scandium, yttrium, lanthanum, and ytterbium, are closely related, and that boron is distinctly separated from the other members of the family.

11.8

Odd-series ALUMINIUM

GALLIUM,

INDIUM

THALLIUM. elements Atomic weights

460 27.02 69 1134

203-64
The molecular weights of these eleinents are unknown.
Sp. grs. (approx.)

2-6
5.9

7:5

11.8 Atom. weights 10-5

15.2

173
spec. graus.
Sp. heats

.225
08
-057

*031 Melting points 700o--800°

30°
175°

290° (approx.) Appearance, and White; very malle- Silver-white; crys. White; lustrous; Grey-white; very general physical able and ductile; talline; hard, melts soft.

lustrous; soft; fairly properties. hard; tough; very very easily; rather

malleable and ducsonorous; good con- brittle.

tile; crystalline; ductor of electricity.

may be distilled in

hydrogen. Occurrence and Oxide of aluminium Compounds occur in Compounds occur in Compounds of thalpreparation. occurs as corundum, small quantities in a small quantities in lium occur in small

sapphire, &c. Sili- few zinc blendes. certain zinc blendes. quantities in various
cates occur in clay, Prepared by electro- Prepared by precipi. widely distributed
felspar, &c. in enor- lysing an alkaline tation by means of minerals.
mous quantities. solution of a basic pure zinc from a Prepared by electro-
Prepared by reduc- sulphate.

solution of the sul- lysis of aqueous soluing Al2C162NaCl by

phate.

tion of TINO;, &c.; sodium or potas

by reduction of same sium, or by electro

solution by zinc; or lysis of the fused

by fusing TICI witla salt.

KCN. General chemical Unchanged in air; Oxidised superfici- Oxidised at mode- Oxidises in air at orproperties. thin pieces heated in ally by heating in rately high tempera- dinary temperaair are burnt to oxygen to full red- ture in air.

tures.
Al203.
ness.

Soluble in most di- Combines directly
Superficially oxi- Combines directly lute acids.

with ci, Br, I, P, dised by melting in with CI, Br, and I. Does not decompose and S. oxygen.

Dissolves in acids, water at 100°. Dissolves in Combines at high also in KOHAq, Atom of indium is H2SO4Aq or temperatures with s, with evolution of H. trivalent in the gas- HNO3Aq with evoP, and As, also Atom of gallium is eous molecule InCiz. lution of H. with N. trivalent in the gase

Decomposes water Decomposes water ous molecule GaCl3;

at red-heat with evoat 100°, evolving H. existence of gaseous

lution of H. Dissolves in hot GagCle is doubtful.

Atom is monovalent HCIAq or

in the only knowu H2SO4Aq.

gaseous molecule Unchanged by mol

TICI.
ten KOH or KNO3 ;
but dissolves in boil.
ing KOHAq giving
an aluminate and 11.
Atom of aluminium
is trivalent in the
gaseous molecule
AICI

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General formulae and characters of compounds. The compounds AICI,, (? Ga,Cig), GaCl,, InCl,, and TICI, have been gasified; these formulae are molecular. Al Br, and Al, I. also appear to exist as gases; but from the results of recent work it is probable that at higher temperatures the molecules AlBr, and All, are formed. The formulae given to the other compounds are generally the simplest formulae which express the compositions of the different bodies; they are not necessarily molecular.

The compounds of gallium and indium have not been very fully investigated.

Oxides: M.O,; also InO and probably Gal; also TI O.
Sulphides: M, S,; also TI S.

Haloid compounds: Mcl,, in one case M.Clo; also
GaCl,; also TICI.

Salts: M 3X; also TI X (X = SO,, 2NO, PO,, &c.).

The oxides M,0, are obtained by adding ammonia to solutions of salts of the several metals, and drying and heating the hydrated oxides so formed. The hydrated oxides obtained are A1,0,.3H,0, (? Ga Oz. 3H,0), In, O.,. 31,0, and T1,0 . 1,0. The oxides, and the hydrated oxides, are in

, soluble in water ; but it is possible, by dialysing a solution of A1,Oz. «H,O in Al,Ci, Aq, to obtain an aqueous solution of hydrated aluminium oxide. The hydrates M,0,.2H, O, except T1,0,. H, 0, are soluble in solutions of caustic potash; potassium aluminate, K A1,0,, is obtained by evaporating the solution of aluminium hydrate; the solution of indium hydrate gives a precipitate of the oxide when boiled ; and the solution of gallium hydrate is decomposed by carbon dioxide with precipitation of gallic oxide,

The oxides M,O, all dissolve in acids forming salts M.3X; the thallic salts are very unstable and are easily reduced to thallous salts, TI X.

When thallic hydrate TI,OH,O is suspended in concentrated potash solution and chlorine is passed into the liquid, the hydrate partially dissolves, forming a violet coloured liquid, which possibly contains the potassium salt of a thallium acid; no salts of this hypothetical acid have however been isolated.

Thallous oxide, TI,O, is strongly basic and alkaline. When a solution of thallous sulphate, T1,80,, is mixed with a solution of baryta in the proportion T1,80 : Bao H,, the liquid is filtered from precipitated barium sulphate, evaporated

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and allowed to crystallise, the hydrated oxide T1,0.2H,0 is obtained. When this hydrate is heated to 100° in absence of air T1,0 is formed. Thallous oxide is very soluble in water and the solution closely resembles KOHAq or NaOHAq in its properties; it has a corrosive action on the skin, a hot and burning taste, turns red litmus blue, absorbs and combines with carbon dioxide, and neutralises acids forming thallous salts, T1,X. There can be little doubt that the solution contains the hydroxide TIOH, and that the composition of hydrated thallous oxide is better expressed by the formula 2TIOH.H,0 than by the formula T1,0. 2H,0.

The haloid compounds, MCI,, are obtained ; (1) by 463 heating the elements in chlorine, M = Ga and In; (2) by heating an intimate mixture of the oxides M,O, and carbon in chlorine, M=Al and In; or (3) by adding HCIAq to the hydrated oxides M,03, M = Tl. The other haloid compounds are obtained by similar methods.

The vapour density of aluminium chloride agrees with the formula AlCl,; that of gallic chloride shews that at moderate temperatures the gaseous compound probably consists of molecules of Ga Cl., but at higher temperatures it consists of molecules of GaCl,; gaseous indium chloride has the molecular composition InCI,; thallic chloride has not been gasified, at

Incl 100° it separates into thallous chloride, TICI, and chlorine. The chlorides, MCI,, are all deliquescent solids; they are all, except probably TICI,, partially decomposed by hot water with formation of various oxychlorides of more or less complex compositions. These chlorides all combine with many other chlorides to form double compounds; e.g. AICI, PCI, ; AICI, POCI; AICI.KCI; InC1,.3KCI; TICI.3KCI.

T'hallous chloride, TICI, is formed as a white precipitate when HCIAq is added to a solution of thallous oxide. This chloride is only slightly soluble in water; it has been gasified without decomposition; it combines with various chlorides to form double compounds; the compound 2TICI. PtCl, resembles, and is isomorphous with, 2KCI. PtCl :

The sulphides M,S, are obtained by the direct union 464 of their elements at high temperatures. A compound K,S. T1,S (possibly a thio-thallate of potassium) is produced by heating thallous sulphide (TIS) with sulphur and potassium carbonate. A similar compound of potassium and aluminium sulphides seems to exist.

Thallous sulphide, Tl,s, is obtained by the direct union

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of its elements, or by adding sulphuretted hydrogen, or ammonium sulphide, to a neutral solution of a thallous salt. A compound Ti,S. As,Sz, analogous to KZS. As,Sz, is known.

Salts of the form M 3X (X=SO,, 2NO,, CO,, PO,, &c.) are obtained by dissolving the different hydrated oxides, M.O, XH,, in acids and evaporating. The salts are generally soluble in water; the thallic salts are easily decomposed, sometimes even by solution in water, and are readily reduced to thallous salts, Tl,X. The sulphates, with the exception of thallic sulphate, combine with sulphates of the alkali metals to form alums, M.350,.X,SO,. 24H,0 (X = alkali metal except Li.) Thallous sulphate (T1,SO) forms an alum with aluminium sulphate, Al,.380,. TI SO :24H,O.

Several basic salts of aluminium, and a few of the other elements, are known.

The thallous salts, T1, X, are generally stable bodies; they are similar to, and usually isomorphous with, salts of potassium.

Of the four odd-series elements of Group III., three, viz. aluminium, gallium, and indium, are evidently very closely related; the fourth, thallium, is to a great extent separated from the others.

Thallium shews marked similarities with the alkali metals which belong to Group I.; at the same time the properties of some of its compounds-e.g. the acidic character of TI,Sz, and the probable existence of an unstable potassium thallatesuggest relations with the most negative element of Group III., viz. boron.

Boron, which is the first member of the group, to some extent summarises the properties of the other members. Oxide of boron is acidic; aluminium oxide is acidic towards strong alkalis; the solubility of Ga,0,. «H,0 and In,0g.<H,0 in concentrated potash solution shews that these oxides have feebly inarked acidic functions; an acidic oxide of thallium probably exists. Oxide of boron also shews basic functions towards some acidic oxides, e.g. So, and P,0s; all the other oxides of

are basic towards most acids. The positive character of boron is shewn in its interaction with steam at high temperatures.

Neither the group-character nor the family-character distinctly preponderates in Group III. The even-series elements from scandium to ytterbium form a closely related class; the odd-series elements from aluminium to indium are

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also very similar; boron at one end of the group, and thallium at the other, are separated from the other members of the group; although differing widely in most of their properties, boron and thallium approach each other in some respects.

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